Hybridization of covalent organic frameworks and photosensitive metal-organic rings:A new strategy for constructing supramolecular Z-scheme heterostructures for ultrahigh photocatalytic hydrogen evolution

The rational design of Z-scheme heterojunction photosystems based on covalent organic frameworks(COFs)is a promising strategy for harnessing solar energy for hydrogen conversion.Herein,a direct Z-scheme single-atom photocatalyst based on COF and metal-organic ring has been constructed through the supramolecular interactions of coral-like COF(S-COF)and photosensitized Pd2L2 type metal-organic ring(MAC-FA1).The MAC-FA1/S-COF heterojunction exhibits good light absorption,efficient charge separation and transfer,slow electron-hole recombination,and highly dispersed Pd active sites,enabling an efficient and stable H_(2) evolution reaction.The optimized 4%MAC-FA1/S-COF achieves an H_(2) evolution rate of 100 mmol g^(−1)h^(−1)within 5 h and obtains a total accumulated turn-over number relative to Pd(TON_(Pd))of 437,685 within 20 h,far superior to S-COF,MAC-FA1,M-5/S-COF,Pd/S-COF,and M-5/Pd/S-COF,which is one of the highest records among COF-based photocatalysts for solar-driven H_(2)evolution.This is the first work to incorporate photosensitized metal-organic rings/cages into porous crystalline COFs to form a supramolecular Z-scheme heterojunction,which has significant potential as a high-performance photocatalyst for solar-driven H_(2)production.